777 fuel leak

[jack744]

Can anyone please explain the symptoms / indications of a tank leak as opposed to an engine fuel leak in the 777 or similar fuel systems?

How would I know which one it was?

Many thanks

[BOAC]

Have a look?

[LME (GOD)]

a drip from the wing?????

[easaman]

B777 tank fuel leak

The O-rings at the fuel boost pump just outboard of the gear tend to leak. As long as the wing is cold soaked, no problem, but ....
Other possibilities are loose tank entry plates.

[email protected]

[jack744]

Ha- yeah

Apologies, I meant from the cockpit in flight. In terms of CALC /TOT, total fuel descrep etc?

Thanks thou

[Paishinel]

Correct me if I am wrong; I did come across a bulletin a long time ago that the Boeing B777 QRH non-normals on fuel leak assumes an engine fuel leak if the leak rate exceeds 1000lbs per 30 minutes. As such one can possibly shut down a good engine when there is a leak from the tank ( assume no visual sighting of leak ) or from the fuel manifold prior to the spar valve.
Queries to Boeing receive an ambiguous and non definitive reply that the ECL and QRH procedures are sufficient to address all fuel leak scenarios. This has led to many to assume that leaks from fuel manifold before the spar valves or fuel tank leaks as improbable without visual detection. Sadly there are too many " ASS U ME " s here

[jack744]

Thanks Paishinel

This is exactly my point. The checklist calls for an engine shutdown but this certainly won't help if it's a tank leak......

[flightleader]

That checklist is only meant for engine fuel leak,read the condition properly.Somehow I think a more appropriate title should be used.

[Bullethead]

That's why the title of the checklist is ENGINE FUEL LEAK CHECKLIST, there's nothing much you can do about a leaking fuel tank.

If it's an engine leak and you can stop it by shutting the engine down and closing the spar valve at least you haven't lost much useable fuel.

However if it's a tank leak about all you could do is feed all engines from the leaking tank until it's almost empty and then switch to the good tank.

Regards,
BH.

[BOAC]

jack - there is NO way you will know from the cockpit. You will have to get out of your seat and go and have a look.

[jack744]

Thanks

Thanks guys - appreciate the input

I do understand the need for a visual inspection. The checklist is designed for an engine leak alone and no, nothing for a tank leak. If the checklist is therefore followed to the T you may not have the desired result.

The 200 assumes a centre tank issue if I'm not mistaken but the 300 is a little different.

I am merely seeking advice from the more experienced of you that have considered this situation

[787cruiser]

B777 fuel leak

I know a former colleague who had an actual engine fuel leak. As far as I can remember he stated that he was unable to ascertain whether it was a tank fuel leak or engine fuel leak. From the ECL and QRH non-normal checklist, he knew that the latter portion of it addressed an engine fuel leak but conditional on visual observation or the leak rate of more than 1000lbs per 30 minutes. As the leak rate was far less than 1000lbs per 30 minutes and there was no visible sighting ( night flight ), he was unable to definitely nail it as an engine fuel leak. Due to the frequent fluctuations in fuel totaliser quantities very common on the B777, even with inflight real time data transmissions of aircraft engine and fuel parameters to maintenance control, the maintenance and engineering personnel were convinced that it was a false alarm due to totaliser fluctuations and he was instructed to continue to destination by both the dispatch and maintenance controllers. As the difference in left and right wing tank burn off ( as per the checklist ) was only about an average of 200lbs-500lbs per 30 minutes and no visible sign of any fuel leak from engines and tanks, he was reluctant to conclude that it was an engine fuel leak, but he was fully convinced that there was a fuel leak somewhere. He countermanded company despatch and maintenance instructions and diverted to a suitable alternate but kept the engine on the suspected side at reduced thrust, with plans to fully shut it down once he get confirmation from airport safety inspection vehicles after landing. Due to ETOPS considerations and possible lightning activities he chose not to shut down or proceed to the nearest alternate. After landing, airport safety vehicle found a small fuel leak from one of the engines and he promptly shut it down right after touchdown. For all his efforts he was grounded and a " kind of punished " for countermanding company instructions. The company claimed in its findings that Boeing recommended following the QRH and ECL closely with the ambiguous remark that the checklist addresses and assumes engine fuel leak, not other fuel leaks. His contention that fuel leak was far less than the criterion of 1000lbs per 30 minutes was not addressed and so were the possibility of tank or manifold leaks were similarly dismissed. Similarly his contention that the checklist did not have a an indent to definitively define it as an engine checklist were rejected. So as we can see, Boeing checklists do have grey areas and pitfalls.

[jack744]

many thanks

Thanks very much cruiser - Good info

[Brian Abraham]

For all his efforts he was grounded and a " kind of punished " for countermanding company instructions.

Worrying. Management face saving? Not their asses or licence on the line. Fuel leaking any where is a problem, and who's to say that a seemingly minor leak is not about to turn into a gusher. Absolute correct decision made by the crew in my humble opinion.

[flightleader]

Bullethead,

My QRH checklist is only titled as Fuel Leak,is yours different?

[Bullethead]

G'day Flightleader,

I was just going on my experience with other Boeing aircraft I have flown where the checklist specifically mentions 'engine fuel leak'. I haven't flown the 777 so I don't have specific knowledge of that aircraft.

Does the B777 'fuel leak' check list cover both engine and tank leaks? If so I'd be interested to know what action is recommended for a tank leak.

Regards,
BH.

[gimmesumvalium]

This subject has always intrigued me because of the before-mentioned grey areas. My comments refer ONLY to B767 and any corrections are welcome.

My thinking is, 3 possible areas to be identified for the leak:
1. Downstream of the Engine Valve, in which case possible indications are higher fuel flow and greater Fuel Used (FMS) on the affected side. Engine Fuel Leak, which the Engine Fuel Leak Checklist should resolve by shutting down the engine.

2. Between Engine Valve and Spar Valve, in which case the only indication is affected Tank quantity reducing at a greater rate. Fuel Flow and Fuel Used (FMS) indications would be normal. Carrying out the Engine Fuel Leak Checklist should resolve by shutting down the engine (closes both the SparValve and Engine Valve).

3. Prior to the Spar Valve (and somewhere in the tank area); after shutting down the engine as per the Engine Fuel Leak Checklist, the indicated fuel quantity continues to reduce. Boeing does not address this situation and provides no guidance. Perhaps, the catch-all 'Commander's judgement' could be applied here, with the POSSIBILITY of re-starting the engine and consuming the remaining fuel (remembering that shutting the engine down did not resolve the initial problem).

An interesting incident was the 777-200ER departing LHR about 3 or 4 yrs ago streaming fuel out of the center tank via the Left Wheel Well. This was observed by the tower, other aircraft and left a 2 nm plume. It was caused by a 2.5 inch opening in the aft wall of the Center Tank at approx the 30,000 kg level. The opening was a Purge Vent and the cover plate had not been re-installed! Lucky there was no Rejected Take Off as the resulting brake temps would have ignited the fuel.

Input please.........

[BOAC]

Originally Posted by gimmesumvalium

Perhaps, the catch-all 'Commander's judgement'

- yes, the best solution would be to restart the engine and cross-feed the other from the leaking tank if fuel is critical - BUT be careful not to lose both!

[160knots]

Out of interest what would be the max fuel imbalance allowed and still maintain controlability, when running both engines from the same tank?

[jack744]

Thanks BOAC /gimmesumvalium

Good info - In fact the 777 is very similar in terms of the fuel/ engine relationship.

I find in interesting that Boeing only issues information for engine leak only and that the checklist only allows for this option. I guess as you say, if you follow the checklist and subsequently the fuel continues to indicate a loss - you would determine it may be a tank problem and crossfeed to the good engine. (even restart)....FMC fuel remaining would be useless and some quick calculations would be necessary


Practically speaking - a visual inspection may show up nothing. In the incident mentioned the pilots only knew of the leak after they were alerted from another aircraft at the hold point (due centre tank)

Cheers